1. Field of the Invention
The present invention relates to a substrate for a transfer mask which is adapted for use in an exposure process using a charged beam such as electron beam or ion beam. The present invention relates also to a transfer mask and to the manufacturing method of the transfer mask.
2. Description of the Related Art
Recently, electron beam lithography, ion beam lithography, etc., where an electron beam or ion beam is employed as an exposure light source, have come to be seen as useful in a technique for manufacturing elements having an ultrafine pattern of the next generation. In the exposure process utilizing these manufacturing techniques, it is required to employ a transfer mask. In the manufacture of this transfer mask, a substrate formed of an SOI (Silicon On Insulator) substrate is employed because of the easiness in fine working.
This SOI substrate for forming a transfer pattern is constituted by a lower monocrystalline silicon wafer as a substrate, a silicon oxide film formed on the lower monocrystalline silicon wafer and functioning as an etching stopper, and an upper monocrystalline silicon wafer formed on the silicon oxide film, the transfer pattern being formed on the upper monocrystalline silicon wafer.
The thickness of silicon oxide film constituting part of the SOI substrate to be employed as a substrate for a transfer mask is generally within the range of about 1 xcexcm to 2 xcexcm. However, there is a problem in the employment of the SOI substrate comprising a silicon oxide film having such a magnitude of thickness that cracks tend to be formed in the upper monocrystalline silicon wafer due to stress imposed thereon by the silicon oxide film, thereby destroying the transfer pattern and hence deteriorating the manufacturing efficiency of the transfer mask.
Therefore, an object of the present invention is to provide a substrate for a transfer mask, which comprises a couple of silicon layers laminated with a silicon oxide film being interposed therebetween, and which makes it possible to stably manufacture a defect-free transfer mask, i.e. a transfer mask wherein a transfer pattern formed on the upper silicon layer is prevented from being destroyed due to stress from the silicon oxide film on the occasion of manufacturing a transfer mask by making use of the substrate.
Another object of the present invention is to provide a transfer mask which comprises a transfer pattern formed on the upper silicon layer of the aforementioned substrate for a transfer mask, and which makes it possible to prevent the transfer pattern formed on the upper silicon layer from being destroyed due to stress from the silicon oxide film on the occasion of manufacturing the transfer mask, thereby providing a defect-free transfer mask.
A further object of the present invention is to provide a method of manufacturing the aforementioned transfer mask, which makes it possible to prevent the transfer pattern formed on the upper silicon layer from being destroyed due to stress from the silicon oxide film, thereby enabling a defect-free transfer mask to be manufactured.
According to the present invention, there is provided a substrate for a transfer mask, which comprises a first silicon layer formed of monocrystalline silicon; a silicon oxide film formed on the first silicon layer and having a thickness ranging from 0.2 to 0.8 xcexcm; and a second silicon layer formed on the silicon oxide film.
According to the present invention, there is further provided a transfer mask comprising a first silicon layer formed of monocrystalline silicon; a silicon oxide film formed on the first silicon layer and having a thickness ranging from 0.2 to 0.8 xcexcm; and a second silicon layer formed on the silicon oxide film and bearing therein a transfer pattern; wherein openings are formed in the first silicon layer, and the portions of the silicon oxide film which correspond to the openings are removed.
According to the present invention, there is further provided a method of manufacturing a transfer mask, the method comprising: preparing a substrate comprising a first silicon layer formed of monocrystalline silicon, a silicon oxide film formed on the first silicon layer and having a thickness ranging from 0.2 to 0.8 xcexcm, and a second silicon layer formed on the silicon oxide film; forming a transfer pattern on the second silicon layer; forming openings in the first silicon layer before or after forming the transfer pattern; and selectively removing portions of the silicon oxide film which correspond to the openings.
According to the present invention, there is further provided a method of manufacturing a transfer mask, the method comprising: preparing a substrate comprising a first silicon layer formed of monocrystalline silicon, a silicon oxide film formed on the first silicon layer and having a thickness ranging from 0.2 to 0.8 xcexcm, and a second silicon layer formed on the silicon oxide film; forming openings in the first silicon layer; selectively removing portions of the silicon oxide film which correspond to the openings; and forming a transfer pattern in the second silicon layer.
According to the present invention, there is further provided a method of irradiating a charged particle beam, the method comprising: irradiating a charged particle beam onto the aforementioned transfer mask in such a manner as to shape the charged particle beam in conformity with the configuration of a transfer pattern; and image-forming a pattern of the shaped charged particle beam on a substrate through a lens.
It is preferable in the present invention that the second silicon layer has a film thickness of 0.1 to 50 xcexcm. Further, the second silicon layer should preferably be formed of monocrystalline silicon.
The substrate for a transfer mask according to the present invention should preferably be formed of an SOI substrate comprising two monocrystalline silicon wafers superposed on one another via a silicon oxide film being interposed therebetween.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.